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Factors influencing the activity of mosquito control agent (Bacillus thuringiensis subsp. israelensis)

Abdoarrahem, Mostafa Mohamed Omar. 2010. Factors influencing the activity of mosquito control agent (Bacillus thuringiensis subsp. israelensis). PhD Thesis, Cardiff University.

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For toxicity, B. thuringiensis must be taken into the larval midgut, where a community of other bacteria is already present. The culturable flora from the Aedes aegypti mosquito midgut was analysed and its role in larval growth and insect mortality was determined. In contrast to published reports concerning B. thuringiensis subsp. kurstaki, subsp. israelensis caused toxicity and larval death even in the absence of other bacteria. The pBtoxis plasmid of B. thuringiensis subsp. israelensis encodes all the mosquitocidal toxins and a number of other coding sequences. The potential effects of selected genes on host phenotype was assessed. No evidence was found for antibiotic production from putative antibiotic synthesis genes. The plasmid also carries potential germination genes organised in a single ger operon. Comparison of the germination responses of spores from strains with and without pBtoxis revealed that this plasmid could promote activation of the spores under alkaline conditions but not following heat treatment. Introduction of the ger operon on a recombinant plasmid to the plasmidless strain established this operon as the first with an identified role in alkaline activation. Mosquito midgets provide an alkaline environment and in which enhanced germination may occur. Co-feeding experiments showed that in competition to colonise intoxicated A. aegypti larvae, B. thuringiensis carrying pBtoxis, are able to outgrow the plasmid-cured strain. This indicates a selective advantage for the presence of pBtoxis. The strain carrying the recombinant ger genes also outgrew its plasmidless parent, indicating that the ger genes may be responsible for this effect, perhaps by allowing strains a head-start by germinating more rapidly in the insect gut.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > QH Natural history > QH301 Biology
Date of First Compliant Deposit: 30 March 2016
Last Modified: 09 Jan 2018 17:12

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